1. Field of the Invention
This invention relates to a temperature control device provided in a plastic-processing machine, which comprises a plasticizing cylinder provided with a nozzle. The temperature control device comprises at least one pair of shell sections, each of which comprises an inside peripheral contacting surface and an outside peripheral surface, which is approximately concentric to the contacting surface. Strap means are provided, which force said shell sections against an outside peripheral surface of a part of the machine which is to be temperature-controlled. The shell sections of said pair or of each of said pairs constitute a heat transfer shell, which encloses the outside peripheral surface of the machine part. Each shell section consists of a metal casting and contains at least one temperature control element, which is embedded in the metal casting of said shell section and has been formed from linear tubes so that said temperature control element constitutes at least one loop having two linear legs and a curved bight connecting said legs. Said loop is approximately symmetrical to a generatrix of the shell section.
In that context the term "temperature control device" is used to describe a device which is adapted to transfer heat at such a rate and with such a timing to and from the plasticizing cylinder and the nozzle that the temperatures required in accordance with the working program of the machine will always be obtained.
The term "tubular temperature control element" is used to describe an element which supplies or extracts thermal energy. In the former case that element consists of a bent resistance heating tube, in which at least one resistance wire is approximately centrally embedded in a powder which is electrically insulating but has a high thermal conductivity. In the second case the element consists of a metal pipe for conducting a liquid coolant.
The invention relates also to a process of manufacturing such a temperature control device.
2. Description of the Prior Art
A temperature control device of that kind is known from U.S. Pat. No. 3,317,958. In that known device, each shell section of the heat transfer shell contains two radially offset temperature control elements, one of which is a tubular heating element and the other a tubular cooling element. The two temperature control elements permit an optimum operating temperature in a relatively large temperature range to be maintained in an object which is to be heated. The wall thickness of each shell section is related to the diameters of the tubular heating element and of the associated cooling element contained therein as 6:1 and 3.5:1, respectively. This means that the known shell section has a relatively large wall thickness and, as a result, a high stiffness so that it is difficult to establish a snug contact between the contacting surface of the shell sections and the outside peripheral surface of the cylindrical object which is to be heated even if additional measures are adopted to reduce the stiffness of said shell sections. For that purpose each shell section of the known device is formed with axial grooves although such grooves result in a higher flexibility only close to the axial grooves rather than in the sectors between the axial grooves.
It is conventional in injection molding machines that the tubular resistance heating elements may directly be pressed onto the outside peripheral surface of the plasticizing cylinder (see e.g., DE 37 36 612 A1; U.S. Pat. Nos. 4,730,937, 4,479,048).